If one of those parameters is tracked it will be saved or even updated in an later request within the same visit. For that the plugin extends the 'log_visit'-table within installation. Its adds three columns at the end of the table.

The plugin uses the translations and is available in english and german.

I'll attach some screenshots and the sourcecode.

Feel free to test, review and comment.
Suggestions for improvements or additional features are welcome ;)

This looks very interesting! This is a very interesting third party plugin.

The code is great, I have nothing to say (which is rare ;-))

One performance improvement could be to have the UPDATE done by the main piwik UPDATE (on log_visit table). If you want to submit a patch to have a hookable UPDATE please do so, I'll commit it to trunk.

If you are interested in contribute more to Piwik, you are very welcome! Great developers are not easy to find ;)

Just added the new version. It now uses the hookable update and includes some small fixes.
Known "Bug":

Displaying the average age in a period other than day doesn't work.
I'm looking for a way to calculate the average value for a given period. There isn't such a feature in the archive processing at the moment.

I have some websides and only 1x the code is included for the Plugin in the Trackingcode.
If the Plugin is active only the side is evaluated in Piwik
var (user) code includes.
But it is evaluated only from the moment in the contained variable
Data are in it.
Is this normaly?

It is only possible to display values after the extended tracking code has been included. Before no additional data has been saved. What do you mean with only the site where the extended tracking code is included evaluates? Does only the community plugin show no data for the rest, or is even the hole tracking not working?

No, I have in log_visit no new entry with aktiv Community Plugin.
Because my Goals don't work any more since 6.4 it can be also a Piwikproblem what can be repaired in 6.5.
(With aktiv Goals the Rest of Piwik is working)

Unfortunately, I have installed your Plugin only with 6.4 and have no possibilities of comparison

At first I had a installerror, DB-Fields without Null by userid and gender, and than I found
as soon as I have an entry in birtdate Piwik stops Tracking.
I have in my Community Mysqlfields with char(10) and date, both with yyyy-mm-dd at least
I tested your example code.
Do you have an idea what I'm doing wrong?

request example will look something like that :
http://my_server/piwik/piwik.php?idsite=1&rec=1&_cvar={"1":["userid","myuser"],"2":["gender","F"],"3":["birthdate","2000-01-25"]}

3)To display the graphic presentation of the previous plugin (use the community folder) , i'm copying the date into the "OLD" data columns , using the following trigger :

create trigger Community_trigger
before insert on piwik_log_visit
for each row
begin
IF NEW.custom_var_k1='userid' THEN SET NEW.userid = NEW.custom_var_v1 ;
END IF;
IF NEW.custom_var_k2='gender' THEN SET NEW.gender = NEW.custom_var_v2 ;
END IF;
IF NEW.custom_var_k3='birthdate' THEN SET NEW.birthdate = NEW.custom_var_v3 ;
END IF;
end$$